MRI features of tibiofibular joint dislocation

Sir, Isolated anterolateral dislocation of the proximal tibiofibular joint (PTFJ) is an uncommon knee injury that can be treated effectively without surgery if diagnosed early [1]. There are four types of PTFJ dislocations, classified by Ogden: subluxation (type 1), anterolateral dislocation (type 2), posteromedial dislocation (type 3) and superior disloca‐ tion (type 4) [1]. A 35-year-old pregnant woman who was taken to our Emergency Department had fallen downstairs, injuring her right knee. On examination she had tenderness and accentuation of the bony prominence of the fibula head, no effusion and pain in the knee joint itself and full range of movement. The peroneal nerve was intact. Radiographs did not show any fractures but revealed some anterior and lateral translation of the fibula head. It has to be mentioned that the diagnostic value of the X-raytechnique is limited in PTFJ dislocations because films exposed in mild degrees of obliquity are difficult to interpret and there are several anatomical variants of the PTFJ and its dislocations [2, 3]. Because of the patient’s pregnancy, MRI instead of CT was performed. Our images were obtained by a T2-weighted turbo-spin echo (TSE) sequence without and with fat suppression (Fig. 1). They showed the ligament injuries in addition to the dislocated fibula, with a triangular gap between the two articulation surface areas. The fibula was in a lateral and slightly anteriorly displaced position and somewhat rotated internally. The weaker posterior tibiofibular ligament was torn. Intact parts of the injured joint capsule and the anterior tibiofibular ligament inhibited a longer dislocation. Such conditions could potentially lead to misdiagnosis in CT scans. In accordance with Ogden’s clas‐ sification an anterolateral PTFJ dislocation, which is the most common variant [1], was diagnosed. A closed reduction under sedation and fluoroscopy-guided conditions was performed. By forceful pressure on the fibula, with the knee in approximately 70° of flexion, the fibula head was reduced with an audible ‘crunch’. The patient felt immediate resolution of symptoms and was allowed to be mobile using a support bandage. To confirm PTFJ dislocations suspected on plain radiographs, axial CT scanning is recommended. However, in the study by Keogh et al. only 71% of the anterolateral dislocations were detected by CT [3]. That might be the result of not completely disrupted tibiofibular ligaments, which hold the fibula fixed in only a lateral displaced position. In atypical cases a comparison with a CT scan of the opposite PTFJ appears to be necessary to M. Zoller . P. Reittner . G. Schaffler (*) Department of Radiology, University Hospital of Graz, Auenbruggerplatz 9, 8036 Graz, Austria e-mail: gottfried.schaffler@meduni-graz.at Tel.: +43-316-38581716 Fax: +43-316-3853231